Aerogel substrate and method for preparing the same

ABSTRACT

An aerogel substrate useful for an electrically conductive substrate, a heat insulating substrate, an optical waveguide substrate, a substrate for a light emitting device or a light emitting device is provided. 
     The aerogel substrate is characterized by comprising a functional layer and an aerogel layer, and an intermediate layer formed between the functional layer and the aerogel layer to allow the functional layer to be formed uniformly thereon. The intermediate layer is formed on at least one surface of the aerogel layer by a gas phase method, by the Langmuir-Blodgett method or by adsorption of an inorganic layered compound; or formed by a hydrophilicizing treatment of at least one surface of the aerogel layer followed by coating and drying an aqueous coating fluid, by an annealing treatment of at least one surface of the aerogel layer, or by a hydrophilicizing treatment of at least one surface of the aerogel layer.

TECHNICAL FIELD

The present invention relates to an aerogel substrate comprising anaerogel layer and a functional layer formed on a surface of the aerogellayer and a process for the production of the substrate.

BACKGROUND ART

An aerogel, particularly a silica aerogel has characteristic propertiessuch as a heat insulating property, an electrically insulating property,a low refractive index and a low dielectric constant. Studies have beenmade to apply the aerogel to various fields using its properties. Forexample, a highly functional substrate can be manufactured by forming athin film of a silica aerogel on a surface of a plate member such as aglass plate and so on and further forming a functional thin film on asurface of the silica aerogel thin film. For example, in the case wherean electrically conductive metal (such as copper) thin film is formed asthe functional thin film on the surface of the silica aerogel thin filmand a circuit is formed with the electrically conductive metal thinfilm, a circuit board can be obtained in which the low dielectricconstant of the silica aerogel is utilized.

The silica aerogel is prepared by hydrolyzing an alkoxysilane (which isreferred to also as a silicon alkoxide or an alkyl silicate) followed bypolycondensation of the alkoxysilane to obtain a gel compound, anddrying the gel compound in the presence of a dispersion medium undersupercritical conditions exceeding a critical point of the solvent, asdisclosed in U.S. Pat. Nos. 4,402,927, 4,432,956 and 4,610,863. Further,as disclosed in Japanese Patent Kokai Publications Nos. 5-279011 and7-138375, a hydrophobing treatment (a treatment for making a silicaaerogel hydrophobic) improves moisture resistance of the silica aerogeland prevents deterioration of characteristic properties of the silicaaerogel.

DISCLOSURE OF INVENTION

In order to produce a highly functional substrate using an aerogel suchas a silica aerogel, it is required that a functional thin film isformed uniformly on a surface of the aerogel. However, it is difficultto form the thin film uniformly on the surface of the aerogel since theaerogel is a porous material. For this reason, a highly functionalsubstrate in which an aerogel is used has not currently been put to itspractical use.

The present invention has been accomplished in the light of thecircumstances as described above, of which object is to provide anaerogel substrate which comprises an aerogel layer and a functionallayer formed uniformly on a surface of the aerogel layer, and a processfor producing the aerogel substrate.

In the first aspect, the present invention provides an aerogel substratewhich comprises an aerogel layer, an intermediate layer which is formedon at least one surface of the aerogel layer and a functional layerwhich is formed on a surface of the intermediate layer, the functionallayer being formed on the surface of the intermediate layer withoutpenetration of a material constituting the functional layer into theaerogel layer.

“Without penetration of a material constituting the functional layerinto the aerogel layer” means that penetration of the material(s) whichconstitutes the functional layer into the aerogel layer through pores inthe aerogel layer does not occur during and after formation of thefunctional layer. Such functional layer constitutes the aerogelsubstrate as a uniform layer (e.g. a thin uniform film) of which surfaceis continuous with a small surface roughness and performs apredetermined function well.

The aerogel substrate of the present invention is obtained by making theintermediate layer as a layer which prevents the material(s) whichconstitutes the functional layer from penetrating into the aerogellayer. “Preventing the material(s) which constitutes the functionallayer from penetrating into the aerogel layer” means preventing thematerial(s) which forms the functional layer from penetrating into theaerogel through the pores in the aerogel layer during and after theformation of the functional layer. In the case where the formation ofthe functional layer involves a material which does not remain in thefunctional layer ultimately (for example, a solvent which evaporates bydrying), the intermediate layer prevents also the penetration of suchmaterial. Therefore, the functional layer which is formed on the surfaceof the intermediate layer is a uniform layer (e.g. a thin uniform film)of which surface is continuous with a small surface roughness.

It is not necessarily needed that the intermediate layer completelyprevents the penetration of the material(s) which constitutes thefunctional layer into the aerogel layer. As long as the functional layeris formed so uniformly that it can perform a desired function dependingon its use or the like, it is acceptable that only a small amount of thematerial(s) constituting the functional layer penetrates into theaerogel layer. For example, in the case where the intermediate layer isnot continuous in a part thereof and micropores (such as pinholes) areformed in the intermediate layer, even if the material(s) constitutingthe functional layer penetrates into the aerogel layer through themicropores, such penetration is accepted as long as the functional layeris formed uniformly as a whole and performs the desired function.

Alternatively, the aerogel substrate according to the present inventionmay be constructed by combining a specific intermediate layer with aspecific aerogel layer and further selecting a specific material(s)which constitutes the functional layer (such as specific material(s)including a material (such as a solvent to be evaporated by drying)which is used only in the step of forming the functional layer), so thatthe material(s) constituting the functional layer may penetrate into theintermediate layer, but cannot penetrate into the aerogel layer from theintermediate layer. Such aerogel substrate is realized, for example, bymaking properties of the intermediate layer different from those of theaerogel layer so that the material(s) constituting the functional layerhas an affinity for the intermediate layer and does not have an affinityfor the aerogel layer.

In any aerogel layer, the intermediate layer may be a layer which isseparately formed on a surface of the aerogel layer, or a layer which isformed by transmuting a part of the aerogel layer. The intermediatelayer which is formed by the transmutation of the aerogel layer issubstantially inseparably unified with the aerogel layer which is nottransmuted, but it is not included in the “aerogel layer” whichconstitutes the aerogel substrate of the present invention. However, inthe case where the intermediate layer is formed by the transmutation ofthe surface of the aerogel layer, “a surface of the aerogel layer”refers to a surface of the intermediate layer so far as a particularmention is not made.

Any one of the aerogel substrates of the present invention can be saidto be a functional substrate of which functional layer can perform apredetermined function. In this specification, the term “substrate” isused in a sense as including a plate member (including a plate, a sheetand a film) of which thickness dimension is considerably smaller thanthe other dimensions, and a rectangular solid and a cube which have athickness dimension which is of generally the same order as those of theother dimensions. The substrate includes a plate, a rectangular solidand a cube in which a part of surface is curved. Therefore, each layerwhich constitutes the aerogel substrate may be in the form of a plate, asheet, a film, a rectangular solid, or a cube depending on the finalform of the aerogel substrate.

The embodiments of the aerogel substrates according to the presentinvention will be described below.

In the first aspect of the present invention, the first embodiment ofthe aerogel substrate is an aerogel substrate comprising a hydrophobicaerogel layer, a hydrophilic layer which is formed by subjecting atleast one surface of the hydrophobic aerogel layer to a hydrophilicizingtreatment (a treatment for imparting hydrophilicity), a coating layerwhich is formed on a surface of the hydrophilic layer, and a functionallayer which is formed on the coating layer. In the first embodiment ofthe first aspect, the intermediate layer consists of the hydrophiliclayer which is formed by subjecting the surface of the hydrophobicaerogel layer to the hydrophilicizing treatment and the coating layerwhich is formed on the surface of the hydrophilic layer. “Subjecting ahydrophobic aerogel layer to a hydrophilicizing treatment” meansremoving hydrophobic groups which exist in the hydrophobic aerogellayer, and the hydrophilic layer is a layer in which the hydrophobicgroups have been removed.

In this aerogel substrate, the hydrophilic layer and the coating layerare interposed as the intermediate layer between the functional layerand the aerogel layer and function as a base layer for forming thefunctional layer uniformly. As described below, the hydrophilic layerformed on the surface of the hydrophobic aerogel layer makes it possiblefor the coating layer to be formed thereon uniformly without penetrationof a film-forming component(s) and water into the hydrophobic aerogellayer when the coating layer is formed by coating the surface of thehydrophilic layer with an aqueous solution and/or an aqueous dispersionof the film-forming component(s) followed by drying the solution and/orthe dispersion. The coating layer fills or coats the pores in thesurface of the hydrophilic layer and prevents the material(s) whichconstitutes the functional layer from penetrating into the aerogel layerwhen the functional layer is formed on the surface of the coating layer.

In the first aspect of the present invention, the second embodiment ofthe aerogel substrate is an aerogel substrate comprising a hydrophobicaerogel layer, a hydrophilic layer which is formed by subjecting atleast one surface of the hydrophobic aerogel layer to a hydrophilicizingtreatment, and a functional layer which is formed on a surface of thehydrophilic layer. In the second embodiment of the first aspect, theintermediate layer is the hydrophilic layer which is formed bysubjecting the surface of the hydrophobic aerogel layer to thehydrophilicizing treatment. This aerogel substrate is a variation inwhich the coating layer of the above described first embodiment of theaerogel substrate of the first aspect corresponds to the functionallayer, which is formed directly on the surface of the aerogel layer(i.e. the intermediate layer). In this aerogel substrate, even if anaqueous solution and/or an aqueous dispersion comprising a film-formingcomponent which is coated on the hydrophilic layer may penetrate intothe hydrophilic layer because the surface of the hydrophobic aerogellayer has been transmuted to be hydrophilic, such solution and/ordispersion cannot move from the hydrophilic layer into the hydrophobicaerogel layer. That is, in this aerogel substrate, the combination ofthe materials which form the aerogel layer, the intermediate layer andthe functional layer prevents the material(s) which constitutes thefunctional layer from penetrating into the aerogel layer.

In the first aspect according to the present invention, the thirdembodiment of the aerogel substrate is an aerogel substrate comprisingan aerogel layer, an inorganic layer or an organic layer which is formedby a gas phase method on at least one surface of the aerogel layer, anda functional layer which is formed on a surface of the inorganic layeror the organic layer. In the third embodiment of the first aspect, theintermediate layer is the inorganic layer or the organic layer which isformed by the gas phase method. The inorganic layer or the organic layerformed by the gas phase method fills or coats the pores in the surfaceof the aerogel layer and prevents the material(s) Which constitutes thefunctional layer from penetrating into the aerogel layer when thefunctional layer is formed on the surface of the inorganic or organiclayer. Further, the inorganic or organic layer gives a smooth surface tofunction as a base coat for forming the functional layer uniformly.

In the first aspect according to the present invention, the fourthembodiment of the aerogel substrate is an aerogel substrate comprisingan aerogel layer, a welded layer which is formed by heating at least onesurface of the aerogel layer, and a functional layer which is formed ona surface of the welded layer. In the fourth embodiment of the firstaspect, the intermediate layer is the welded layer which is formed byheating at least one surface of the aerogel layer. The “welded layer” isa layer which has been densified by closing the pores in the aerogellayer. The material(s) which constitutes the functional layer formed onthe surface of the welded layer cannot penetrate into the aerogel layersince the formation of the welded layer closes the pores in the vicinityof the surface of the aerogel layer. The welded layer generally has asmooth surface, which also contributes to uniform formation of thefunctional layer.

In the first aspect according to the present invention, the fifthembodiment of the aerogel substrate is an aerogel substrate comprisingan aerogel layer, a Langmuir-Blodgett film which is formed on at leastone surface of the aerogel layer, and a functional layer which is formedon a surface of the Langmuir-Blodgett film. In the fifth embodiment ofthe first aspect, the intermediate layer is the Langmuir-Blodgett film.The Langmuir-Blodgett film fills or coats the pores in the surface ofthe aerogel layer and prevents the material(s) which constitutes thefunctional layer from penetrating into the aerogel layer when thefunctional layer is formed on the surface of the Langmuir-Blodgett film.The Langmuir-Blodgett film generally has a smooth surface, which alsocontributes to uniform formation of the functional layer.

In the first aspect according to the present invention, the sixthembodiment of the aerogel substrate is an aerogel substrate comprisingan aerogel layer, an inorganic layered compound layer which is formed onat least one surface of the aerogel layer, and a functional layer whichis formed on a surface of the inorganic layered compound layer. In thesixth embodiment of the first aspect, the intermediate layer is a layerof the inorganic layered compound. The inorganic layered compound layerfills or coats the pores in the surface of the aerogel layer andprevents the material(s) which constitutes the functional layer frompenetrating into the aerogel layer when the functional layer is formedon the surface of the inorganic layered compound layer. The inorganiclayered compound layer generally has a smooth surface, which alsocontributes to uniform formation of the functional layer.

In any aerogel substrate of the above first to sixth embodiments of thefirst aspect, the aerogel layer is preferably made of a silica aerogel.

By forming the functional layer as a layer which performs a desiredfunction, it is possible to produce an aerogel substrate of the presentinvention as a desired functional substrate. The functional layer is,for example, an electrically conductive thin film, an infrared rayreflective thin film, an optical waveguide thin film, a transparent andelectrically conductive thin film, or a fluorescent layer.

An aerogel substrate of which functional layer is the electricallyconductive thin film can be used as a circuit board by forming a circuitpattern with the electrically conductive thin film. The electricallyconductive material thereof is an electrically conductive metal which isselected from copper, aluminum, magnesium, silver and the like. Theelectrically conductive material is preferably copper from theviewpoints of electrical conductivity and cost. The circuit pattern isformed by subjecting the electrically conductive metal thin film totreatments including the photoresist formation, the masking, theexposure, the development and the etching.

In the case where the aerogel layer of the circuit board is a silicaaerogel layer, the circuit board can be used as an excellent circuitboard having a low dielectric constant and is useful as a substrate fora large-scale integrated circuit. This is because the silica aerogel hasa very low dielectric constant of about 1.05 to about 2.0.

An aerogel substrate having the infrared ray reflective thin film can beused as a heat insulating substrate since the substrate can reflectinfrared rays. The infrared ray reflective thin film is, for example, athin film of aluminum or titania.

In the case where the aerogel layer of the heat insulating substrate isa silica aerogel layer, a thermal conductivity of the substrate isreduced, and therefore the aerogel substrate shows more excellent heatinsulating properties. This is because the silica aerogel has a very lowthermal conductivity of about 0.01 to 0.025 W/mK and a very low density.

An aerogel substrate having an optical waveguide thin film can be usedas an optical waveguide substrate which transmits a light in apredetermined direction. In this aerogel substrate, a light is totallyreflected at the interface between the aerogel layer and the opticalwaveguide thin film (such as a transparent thin film made of aninorganic oxide), and therefore the optical waveguide thin filmfunctions as an optical waveguide path with a high optical transmissionperformance. The optical waveguide thin film is a transparent filmhaving a large refractive index and made of a material for an opticalfiber, such as silica.

In the case where a dense layer (e.g. film) is disposed as theintermediate layer between the optical waveguide thin film and theaerogel layer as in the aerogel substrates of the first embodiment andthe third to sixth embodiments in the first aspect, a thickness of theintermediate layer is preferably 300 nm or less, and more preferably 100nm or less. If the thickness of the layer is larger than a wavelength ofthe light to be transmitted, the light cannot be transmitted.

In the case where the aerogel layer of the optical waveguide substrateis a silica aerogel layer, a total reflectivity at the interface betweenthe optical waveguide path and the aerogel layer is increased, andtherefore the light transmission loss is considerably reduced even ifthe optical waveguide path is formed into a curved pattern. This isbecause the silica aerogel has a very low refractive index of 1.008 to1.3.

The aerogel substrate having the transparent and electrically conductivethin film can be used as a substrate for a light emitting device. Thistransparent and crystal as well as a function of a touch panel. This isbecause a silica aerogel has a very low refractive index and the sameoptical function as that of air.

An aerogel substrate having the fluorescent layer can be used as a lightemitting device. The light is emitted from the fluorescent layer byirradiation of an ultraviolet ray. Similarly to the light emittingdevice described above, where the aerogel layer is the silica aerogellayer, an external efficiency upon coupling out the light generated inthe fluorescent layer can be increased. The fluorescent layer is madeof, for example, an inorganic fluorescent material such as Y₂O₃:Eu(red), LaPO₄:Ce, Tb (green), BaMgAl₁₀O₁₇:Eu (blue) or the like, or anorganic fluorescent material such as a low molecular weight dyematerial, a conjugated polymer material or the like.

Each layer described above is an example of the preferred functionallayer. The functional layer may perform other function. Further, theterm “functional layer” is used in the sense of including a layer whichgives a desired property to the substrate comprising the aerogel layerand provides a certain effect. For example, the functional layerincludes a colored thin film which is formed so as to give a decorativeeffect to the surface of the aerogel layer.

In the second aspect, the present invention provides a electricallyconductive thin film can be made of a transparent and electricallyconductive material selected from indium-tin oxide (ITO), indium-zincoxide (IXO), silver, chromium and so on. The aerogel substrate havingthe transparent and electrically conductive thin film can constitute,for example, an EL light emitting device. The EL light emitting deviceis formed by providing an EL (electroluminescence) layer on a surface ofthe transparent and electrically conductive thin film of the aerogelsubstrate and providing a back metal electrode on a surface of the ELlayer. The EL layer can be made of a luminescent material conventionallyused in the organic EL or inorganic EL. The light is emitted from the ELlayer by applying an electric field between the transparent andelectrically conductive thin film and the back metal electrode. This ELlight emitting device can be used for various kinds of displays.

The light emitting device in which the aerogel layer is a silica aerogellayer can be used as an EL light emitting device of which externalefficiency upon coupling out the light generated in the EL layer ishigh. This is because the silica aerogel has a very low refractive indexof 1.008 to 1.3. Further, the light emitting device comprising thesilica aerogel layer make it possible to produce a display having afunction of protection of a front light for a reflective liquid processfor producing the aerogel substrate in the first aspect according to thepresent invention.

The process for producing the aerogel substrate of the present inventioncomprises the steps of:

forming an intermediate layer on at least one surface of an aerogellayer; and

forming a functional layer on a surface of the intermediate layer,

said intermediate layer being a layer which prevents a material(s) whichconstitutes the functional layer from penetrating into the aerogellayer.

The aerogel substrates of the first embodiment and the third to thesixth embodiments provided by the present invention in the first aspect,can be produced by forming the intermediate layer according to thefollowing methods.

The process for producing the aerogel substrate of the first embodimentin the first aspect comprises the steps of:

forming a hydrophilic layer by subjecting at least one surface of ahydrophobic aerogel layer to a plasma treatment or a UV ozone treatment;

forming a coating layer by coating a surface of the hydrophilic layerwith an aqueous solution and/or an aqueous dispersion of a film-formingcomponent(s) followed by drying the solution and/or the dispersion; and

forming a functional layer on a surface of the coating layer.

This production process is characterized in that the step of forming theintermediate layer comprises the step of forming the hydrophilic layerby subjecting at least one surface of the hydrophobic aerogel layer tothe plasma treatment or the UV ozone treatment; and forming the coatinglayer by coating the surface of the hydrophilic layer with the aqueoussolution and/or the aqueous dispersion of the film-forming component(s)followed by drying the solution and/or the dispersion.

According to this production process, a surface which is suitable forforming the functional layer uniformly thereon is provided by formingthe coating layer on the surface of the hydrophobic aerogel layer, andthe hydrophilicizing treatment of the hydrophobic aerogel layer makes itpossible to form the coating layer on the surface thereof.

The coating layer is formed by coating the surface of the hydrophiliclayer with the aqueous film-forming component(s) solution and/or theaqueous film-forming component(s) dispersion followed by drying thesolution and/or the dispersion. “Film-forming component” is a componentwhich constitutes a film after a solution or a dispersion containing thecomponent is coated and thereafter dried to remove a solvent. As “theaqueous solution and/or the aqueous dispersion of the film-formingcomponent(s)”,are listed a) an aqueous solution of the film-formingcomponent(s), b) an aqueous dispersion of the film-forming component(s),and c) a fluid containing at least two film-forming components, at leastone component being dissolved in water and at least one other componentbeing dispersed in water.

The aerogel represented by the silica aerogel is porous. When a liquidsubstance is applied onto the aerogel, the liquid substance easilypenetrates into the aerogel due to the capillarity, whereby themicroporous structure of the aerogel may be broken resultingdeterioration of the properties of the aerogel. For the aerogel whichhas not been to subjected to the hydrophobing treatment, its microporousstructure is broken when either of a water-based liquid substance or anoil-based liquid substance penetrates therein. It is substantiallyimpossible to form a film on such aerogel by applying a liquid forcoating.

On the other hand, for the hydrophobic aerogel, i.e. an aerogel to whichhydrophobicity has been imparted, the microporous structure is notbroken by the penetration of the water-based liquid, although themicroporous structure is broken by the penetration of the oil-basedliquid substance. Therefore, no break of the microporous structure iscaused even if a film is formed on the surface of the hydrophobicaerogel using the water-based liquid for coating (i.e. an aqueoussolution and/or an aqueous dispersion of the film-forming component(s))according to the conventional coating method (for example, the spincoating method). However, it is actually difficult to apply thewater-based liquid for coating uniformly on the surface of thehydrophobic aerogel since hydrophobic organic groups which repel theaqueous solution and/or the aqueous dispersion are bound to the surfaceof the hydrophobic aerogel.

In the process for producing the aerogel substrate of the firstembodiment in the first aspect, the organic hydrophobic groups on thesurface of the aerogel are removed by subjecting the surface of thehydrophobic aerogel layer to the plasma treatment or the UV ozonetreatment while its hydrophobicity is maintained in the inside. By theremoval of the hydrophobic groups, a hydrophilic layer is formed in thesurface of the aerogel layer, and thereby the aqueous solution and/orthe aqueous dispersion of the film-forming component(s) as the liquidfor coating can be applied uniformly onto the surface of the aerogellayer and a film-like coating layer is formed after drying to removewater. The coating layer fills or coats the pores in the surface of theaerogel layer and preferably has a smooth surface. There is no casewhere the aqueous solution and/or the aqueous dispersion penetratesinside to break the microporous structure since the inside of theaerogel layer remains hydrophobic.

The plasma treatment can be carried out by a known method conventionallyused for carrying out surface cleaning or the like.

The UV ozone treatment also can be carried out by a known method.Concretely, the treatment is carried out by a method in which the oxygenin the air is ozonized by irradiation of ultraviolet rays to produceoxygen radicals and the aerogel surface is etched and cleaned with theradicals.

The plasma treatment or the UV ozone treatment is preferably carried outsuch that the thickness of the hydrophilic layer in which thehydrophobic groups in the aerogel have been removed is in the range of50 nm to 100 μm.

The process for producing the aerogel substrate of the third embodimentin the first aspect comprises the steps of:

forming an inorganic layer or an organic layer by a gas phase method onat least one surface of an aerogel layer; and

forming a functional layer on a surface of the inorganic layer or theorganic layer.

This production process is characterized in that the step of forming theintermediate layer comprises the step of forming the inorganic layer orthe organic layer by the gas phase method on at least one surface of theaerogel layer.

The gas phase method (or a vapor growth method) is a method for forminga film by evaporating a film-forming material(s) in vacuum or forming aplasma material(s) in vacuum followed by depositing such material(s) ona surface of an object (i.e. the aerogel layer in the present invention)to form a film. Concretely, a CVD (Chemical Vapor Deposition) method, asputtering method, or a vapor deposition (vacuum deposition) can beemployed as the gas phase method.

The inorganic layer or the organic layer which coats or fills the poresin the surface of the aerogel layer is formed by the gas phase method.The smoothness of the surface of the inorganic layer or the organiclayer can be improved by appropriately selecting conditions of the gasphase method. The formation of the inorganic layer or the organic layerby means of the gas phase method does not cause the break of themicroporous structure of the aerogel since the gas phase method is a dryprocess which does not involve coating a liquid substance followed bydrying the substance. Therefore, this production process can be appliedto both of the hydrophobic aerogel or the aerogel which has not beensubjected to the hydrophobing treatment.

The thickness of the inorganic layer or the organic layer formed by thegas phase method is preferably 50 nm to 100 μm.

The process for producing the aerogel substrate of the fourth embodimentin the first aspect comprises the steps of:

forming a welded layer by heating at least one surface of an aerogellayer; and

forming a functional layer on a surface of the welded layer.

This production process is characterized in that the step of forming theintermediate layer comprises the step of forming the welded layer byheating at least one surface of the aerogel layer.

An annealing treatment in which at least one surface of the aerogellayer is heated results in closing the pores in the vicinity of thesurface of the aerogel layer, and thereby a dense intermediate layerwhich is not porous is formed. Heating the aerogel layer is carried outby placing the aerogel layer in a high temperature furnace for severaltens of seconds, or by irradiation of heat rays onto the surface forshort period of time. In any method, heating is preferably carried outsuch that the thickness of the welded layer is in the range of 50 nm to100 μm. This production process can be applied to both of a hydrophobicaerogel or an aerogel which has not been subjected to the hydrophobingtreatment since this method does not involve coating a solution and soon upon making the surface of the aerogel layer smooth.

The process for producing the aerogel substrate of the fifth embodimentin the first aspect comprises the steps of:

forming a thin film on at least one surface of an aerogel layer by theLangmuir-Blodgett method; and

forming a functional layer on a surface of the thin film.

This production process is characterized in that the step of forming theintermediate layer comprises the step of forming the thin film on atleast one surface of the aerogel layer by the Langmuir-Blodgett method.

In this production process, the thin film as the intermediate layer isformed on a surface of the porous aerogel layer by the Langmuir-Blodgettmethod, which film coats or fills the pores in the surface of theaerogel layer. The Langmuir-Blodgett method (which is referred to alsoas “LB method”)is a method for forming a thin film in which method apolymer membrane is formed on a water surface by spreading a polymersolution which is insoluble into water; the surface of the aerogel layeris contacted with the polymer membrane at an appropriate surfacepressure; and thereby the polymer membrane is transferred from the watersurface to the surface of the aerogel.

The thickness of the thin film formed by the LB method is within amonomolecular level, and therefore, the LB method makes it possible toform a very thin film having a thickness of several nanometers or otherswithin the same order. Further, the film thickness can be controlled bythe nanoscale by varying a length of a side-chain of the polymer.Furthermore, as described below, by a built-up technique for building upa polymer thin film on the surface of the aerogel layer such as avertical dipping method or a horizontal dipping method, a built-up filmstructure and properties of the film surface can be changed. Uponforming the polymer thin film by the LB method, as the polymer, apolymer having an amphipatic property which is selected from apolyimide, a polyalkylacrylate, a polyester, a polyvinylacetal, apolyglutamate and so on can be used.

The process for producing the aerogel substrate of the sixth embodimentin the first aspect comprises the steps of:

forming an inorganic layered compound layer by having at least onesurface of an aerogel layer adsorb an inorganic layered compound; and

forming a functional layer on a surface of the inorganic layeredcompound layer.

This production process is characterized in that the step of forming theintermediate layer comprises the step of forming the inorganic layeredcompound layer by having at least one surface of the aerogel layeradsorb the inorganic layered compound.

In this production process, the surface of the aerogel layer on whichthe functional layer is formed is coated with the inorganic layeredcompound layer. The inorganic layered compound layer coats or fills thepores in the surface of the aerogel layer to prevent the material(s)which constitutes the functional layer formed on its surface frompenetrating into the aerogel layer. Generally, the inorganic layeredcompound layer provides a smooth surface to ensure that the functionallayer is formed more uniformly. The inorganic layered compound layer isformed by contacting the surface of the porous body with a treatmentliquid which includes the inorganic layered compound dispersed in asolvent, and thereby having the surface of the aerogel layer adsorb theinorganic layered compound. “Adsorb” means forming the inorganic layeredcompound layer without involving the solvent of the treatment liquid inwhich the inorganic layered compound is dispersed in the formation ofthe inorganic layered compound layer in the course of the formation ofthe layer on the surface of the object (i.e. the aerogel layer in thepresent invention). This production process can be applied to both of ahydrophobic aerogel and an aerogel which has not been subjected to thehydrophobing treatment since this process does not require theapplication of a liquid substance on the surface of the aerogel layer.

In any one of the production processes described above, the functionallayer is formed by a coating method or a gas phase method.

The coating method is a method for forming a film by coating a surfaceof an object with a liquid in which a film-forming component(s) isdissolved and/or dispersed in a solvent followed by drying the liquid toremove the solvent. The coating method is a conventional film formingmethod. Concretely, the spin coating method, the dip coating method, thespray coating method, the bar coating method and the like are known.

The gas phase method is the same as described with respect to theproduction process of the aerogel substrate of the third embodiment inthe first aspect. The gas phase method makes it possible to control thethickness of the layer to be formed to a very thin thickness (forexample, several hundreds of nanometers). Such control cannot beachieved by the coating method.

In the third aspect, the present invention provides a process forproducing the aerogel substrate of the second embodiment in the firstaspect.

The process for producing the aerogel substrate of the second embodimentin the first aspect comprises the steps of:

forming a hydrophilic layer by subjecting at least one surface of ahydrophobic aerogel layer to a plasma treatment or a UV ozone treatment;and

forming a functional layer by coating a surface of the hydrophilic layerwith an aqueous solution and/or an aqueous dispersion of a film-formingcomponent(s) followed by drying the solution and/or the dispersion.

This production process is characterized in that the step of forming theintermediate layer comprises the step of forming the hydrophilic layerby subjecting at least one surface of the hydrophobic aerogel layer tothe plasma treatment or the UV ozone treatment.

This production process is a variation of the production process of theaerogel substrate of the first embodiment in the first aspect whereinthe functional layer is formed directly on the surface of thehydrophilic layer without forming the coating layer. This productionprocess can be applied when the functional layer is formed by applyingthe aqueous solution and/or the aqueous dispersion of the film-formingcomponent(s) followed by drying the solution and/or the dispersion. Theaqueous solution and/or the aqueous dispersion which is used in formingthe functional layer contains a component(s) as the film-formingcomponent(s) which gives a desired function to the substrate. Forexample, a transparent and electrically conductive thin film can beformed as the functional layer by coating the surface of the hydrophiliclayer with an aqueous solution and/or an aqueous dispersion containingindium-tin oxide as the film-forming component followed by drying thesolution and/or the dispersion.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a), 1(b) and 1(c) are respectively cross-sectional views whichschematically show merely examples of the aerogel substrate according tothe present invention;

FIGS. 2(a) and 2(b) schematically show a process for forming a thin filmon a surface of an aerogel layer by the LB method; and

FIGS. 3(a), 3(b) and 3(c) schematically show a process for forming athin film on a surface of an aerogel layer by the LB method.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be explained below.

The aerogel which constitutes the aerogel substrate of the presentinvention includes a gel which is obtained by a supercritical drying ofa wet gel, and a gel which is obtained by drying a wet gel undersubcritical conditions and has a similar structure (generally, aporosity) to that of the gel which is obtained by the supercriticaldrying. The aerogel has preferably at least 40% of porosity, morepreferably at least 60% of porosity, and furthermore preferably at least80% of porosity. The aerogel is preferably a silica aerogel.

The silica aerogel can be produced by obtaining a gel having a silicaframework in a wet state by means of hydrolysis followed bypolymerization of an alkoxysilane (which is referred to also as asilicon alkoxide or an alkyl silicate) and drying the gel in thepresence of a solvent (or a dispersion medium) such as an alcohol orcarbon dioxide under supercritical conditions exceeding a critical pointof the solvent, as described in U.S. Pat. Nos. 4,402,927, 4,432,956 and4,610,863. For example, the supercritical drying may be carried out bydipping the polymerized wet gel in liquefied carbon dioxide so that allof the solvent which the gel contains therein is replaced with theliquefied carbon dioxide of which critical point is lower than that ofthe solvent, followed by removing carbon dioxide under the supercriticalconditions. Alternatively, the supercritical drying is carried out byreplacing a part of the solvent which is contained in the gel with theliquefied carbon dioxide, followed by removing the solvent and carbondioxide under the supercritical conditions of the solvent and carbondioxide system.

Alternatively, the silica aerogel is produced using sodium silicate as astarting material in the same manner as the above, as described in U.S.Pat. Nos. 5,137,927 and 5,124,364.

The silica aerogel is preferably one to which hydrophobicity has beenimparted, i.e. the hydrophobic silica aerogel. It is difficult formoisture and water to go into the inside of the hydrophobic silicaaerogel, and thus, degradation of the properties of the silica aerogelsuch as the refractive index, the light transparency and so on isprevented.

The hydrophobicity can be imparted to the silica aerogel by subjectingthe gel compound obtained by the hydrolysis and polymerization of thealkoxysilane to a hydrophobing treatment, as disclosed in JapanesePatent Kokai Publication Nos. 5-279011 and 7-138375.

The hydrophobing treatment may be carried out before or during thesupercritical drying of the gel compound. The hydrophobing treatment iscarried out by reacting hydroxyl groups of silanol groups which are onthe surface of the gel compound with hydrophobic groups of an agent forthe hydrophobing treatment so that the hydroxyl groups are replaced withthe hydrophobic groups of the agent. Concretely, for example, thereaction for replacing the hydroxyl groups with the hydrophobic groupsis carried out by dipping the gel compound into a hydrophobing treatmentliquid containing a solvent in which the hydrophobing treatment agenthas been dissolved, so that the hydrophobing treatment agent canpenetrate into the gel, followed by heating if necessary.

As the hydrophobing treatment agent, for example hexamethyldisilazane,hexamethyldisiloxane, trimethylmethoxysilane, dimethyldimethoxysilane,methyltrimethoxysilane, ethyltrimethoxysilane, trimethylethoxysilane,dimetyldiethoxysilane, metyltriethoxysilane and so on are exemplified.There is no particular limitation as to the solvent used for thehydrophobing treatment as long as the solvent easily dissolves thehydrophobing treatment agent and also is able to be replaced with thesolvent that the gel material contains before the hydrophobingtreatment. As the solvent which is used for the hydrophobing treatment,for example methanol, ethanol, isopropanol, xylene, toluene, benzene,N,N-dimethylformamide, hexamethyidisiloxane and the like may be used. Inthe case where the supercritical drying is carried out later on, thesolvent is preferably one which is easily dried by the supercriticaldrying, such as methanol, ethanol, isopropanol, liquefied carbon dioxideor the like, or other solvent which is able to be replaced with one ofthose listed solvents.

The refractive index of the silica aerogel is very small since itsporosity is large. Therefore, the aerogel layer made of the silicaaerogel is particularly preferably used where the aerogel substrate is asubstrate for a light emitting device of which functional layer is atransparent and electrically conductive thin film or for a lightemitting device of which functional layer is a fluorescent layer.

The aerogel other than the silica aerogel is a porous material which isobtained by forming a wet gel of a melamine resin followed by thesupercritical drying thereof as described in U.S. Pat. No. 5,086,085.

As the gel which is obtained by drying the wet gel under the subcriticalconditions and has the similar structure to that of the gel which isobtained by the supercritical drying, a porous silica (xerogel) isexemplified which is obtained by means of normal heating or vacuum todry a wet gel which is obtained by hydrolysis and polymerization of analkoxysilane or a gelation reaction of sodium silicate. Japanese PatentKohyo Publications Nos. 8-505674 and 10-508569 disclose a silica whichis produced by drying under the subcritical conditions and has aporosity similar to that of the silica prepared by the supercriticaldrying. Such silica is preferably used in the present invention. Theporous silica may be one which has been subjected to the hydrophobingtreatment as described in U.S. Pat. No. 5,830,387.

Further, a porous material of, for example, a polymethylmethacrylateresin can be used in place of the aerogel which porous material isobtained by preparing a resin mixture of a polystyrene resin and apolymethylmethacrylate resin and then selectively removing thepolystyrene resin by means of its dissolution as described in “SCIENCE”,Vol. 283, 1999, p 520.

The U.S. Patents, the Japanese Patent Kokai Publications, JapanesePatent Kohyo Publications and the technical reference referred to in theabove as to the production process and the hydrophobing treatments ofthe aerogel are incorporated in the present specification with thereferences thereto.

It is difficult to handle the aerogel alone in the form of a sheet or aboard unless the thickness thereof is at least several millimeters sincethe strength of the aerogel is very small. Therefore, the aerogelsubstrate of the present invention may be in the form of a laminate inwhich the aerogel layer is laminated on a plate member. The plate memberis appropriately selected depending on the function which is achieved bythe aerogel substrate as long as the plate member ensures the strengthof the substrate as a whole. The plate member has predetermined opticalproperties (such as a refractive index and transparency) if the aerogelsubstrate becomes a light emitting device or a substrate for the lightemitting device. The plate member may be, for example, a glass plate.

The aerogel layer may be formed on a surface of the plate member forexample according to the following procedures:

(1) An alkoxysilane solution prepared by mixing an alkoxysilane, water,a catalyst such as ammonia, and a solvent, is applied on a surface ofthe plate member;

(2) A gel in the form of a thin film is formed by hydrolysis andpolymerization of the alkoxysilane, and the gel is subjected to thehydrophobing treatment if necessary; and

(3) The gel laminated on the plate member is subjected to thesupercritical drying.

Then, concrete embodiments of the aerogel substrates of the presentinvention are described together with the production processes thereof.

Firstly, the aerogel substrate of the first embodiment in the firstaspect, i.e. the aerogel substrate in which the aerogel layer is thehydrophobic aerogel layer; the intermediate layer consists of thehydrophilic layer which is formed by subjecting at least one surface ofthe hydrophobic aerogel layer to the hydrophilicizing treatment and thecoating layer which is formed on the surface of the hydrophilic layer;and the functional layer is formed on the surface of the coating layer,is explained.

“At least one surface” of the hydrophobic aerogel layer to be subjectedto the hydrophilicizing treatment is usually one of two surfaces of thehydrophobic aerogel layer which are vertical to the direction of thethickness of the aerogel layer. When the hydrophobic aerogel layer islaminated on a surface of a plate member, the surface of the aerogellayer which surface is opposite to the surface in contact with the platemember is generally subjected to the hydrophilicizing treatment. In thecase where the hydrophobic aerogel layer is thick and, for example, inthe form of a rectangular solid or a cube, a surface(s) which isparallel to the direction of the thickness may be subjected to thehydrophilicizing treatment. Two or more surfaces may be subjected to thehydrophilicizing treatment. For example, when the hydrophobic aerogellayer is not laminated on a plate member and used alone, two surfacesvertical to the direction of the thickness may be subjected to thehydrophilicizing treatment. Alternatively, one surface vertical to thedirection of the thickness of the hydrophobic aerogel layer and onesurface parallel to the direction of the thickness may be subjected tothe hydrophilicizing treatment.

In the hydrophilic layer which is formed on at least one surface of thehydrophobic aerogel layer, the hydrophobic groups of the aerogel havebeen removed. Such hydrophilic layer is formed by subjecting at leastone surface of the hydrophobic aerogel layer to the plasma treatment orthe UV ozone treatment.

The plasma treatment is preferably so carried out that the hydrophobicgroups are removed in the portion from the surface of the hydrophobicaerogel layer to a level of a depth of 50 nm to 100 μm. For thispurpose, the plasma treatment is carried out by injecting a plasma froma plasma injecting nozzle onto the surface of the hydrophobic aerogellayer using a plasma treatment apparatus such as an atmospheric pressureplasma cleaning apparatus (manufactured by Matsushita Electric Works,Ltd., trade name “Aiplasma”)with the nozzle spaced by about 7 mm apartfrom the surface of the hydrophobic aerogel layer. The plasma is, forexample a plasma of one or more gases selected from helium, argon andoxygen. Such plasma may be generated using, for example, an electricpower of 700 to 800 W. The surface of the hydrophobic aerogel layer ispreferably subjected to the plasma treatment for 0.1 to 2 seconds.

The UV ozone treatment is also preferably carried out such that thehydrophobic groups are removed in the portion from the surface of thehydrophobic aerogel layer to a level of a depth of 50 nm to 100 μm.Concretely, the UV ozone treatment is carried out by applying a UV rayfrom a UV light source such as an excimer lamp onto the surface of thehydrophobic aerogel layer in an oxygen atmosphere or the air. The timefor which the UV is applied onto the surface of the hydrophobic aerogellayer depends on the power of the UV light source and so on, and it isgenerally in the range of 10 seconds to 1 minute.

The coating layer formed on the surface of the hydrophilic layer isprovided to fill the pores in the surface of the hydrophobic aerogellayer so that the material(s) which constitutes the functional layer isprevented from penetrating into the aerogel layer when the functionallayer is formed on the surface of the coating layer. The coating layeralso removes surface unevenness due to the pores and provides the smoothsurface which is suitable for forming the functional layer thereon.

The coating layer is formed by coating the surface of the hydrophiliclayer with the aqueous solution and/or the aqueous dispersion of thefilm-forming component(s) followed by drying the solution and/or thedispersion. The aqueous solution and/or the aqueous dispersion of thefilm-forming component(s), i.e. an aqueous fluid for coating is preparedby so adjusting the viscosity and so on that the film-formingcomponent(s) uniformly covers the surface of the aerogel to fill thepores in the surface uniformly after the fluid is applied and dried.Concretely, an aqueous solution of a water-soluble polymer such as apolyvinyl alcohol or a polyethylene oxide is preferably used. Theconcentration of the water-soluble polymer is preferably 0.1 to 5% bymass.

Further preferably, the aqueous solution of the water-soluble polymercontains fine particles of silica. In the case where the fine particlesof silica are contained as the film-forming component in the aqueoussolution, the pores which exist on the surface of the hydrophobicaerogel layer are filled with more densely packed fine particles, andthereby a more smooth surface is provided after the formation of thefilm. The aqueous solution of the water-soluble polymer containing thefine particles of silica is obtained by dispersing a silica sol in theaqueous solution. The content of the silica sol is preferably in therange of 5 to 50% by mass, but not limited thereto. The silica sol maybe dispersed in an aqueous solution or an aqueous dispersion other thanthe aqueous solution of the water-soluble polymer.

The aqueous fluid for coating may be applied by the conventional methodsuch as the spin coating method, the dip coating method, the spraycoating method, the bar coating method or the like. After theapplication, the aqueous fluid for coating may be dried with a drier ormay be air-dried.

The thickness of the coating layer which is formed after drying theaqueous fluid for coating is preferably 50 nm to 100 μm.

The coating layer fills the surface pores of the aerogel layer andprovides the smooth surface. Therefore, the functional layer can beformed on the surface of the coating layer uniformly, and thereby it canperform its function sufficiently.

The functional layer is, for example, the electrically conductive thinfilm, the infrared ray reflective thin film, the optical waveguide thinfilm, the transparent and electrically conductive thin film, or thefluorescent layer. Materials for and thickness of the functional layerare so selected that the aerogel substrate as a final product canperform a desired function. The method for forming the functional layeris selected from the gas phase method and the coating method dependingon the materials for and the thickness of the functional layer.

For example, the electrically conductive thin film may be formed by, forexample the vacuum deposition or the sputtering of an electricallyconductive metal such as copper. Generally, the thickness of theelectrically conductive thin film is preferably about 50 to about 200nm.

The infrared ray reflective thin film may be formed by, for example thesputtering or the vacuum deposition of aluminum or titania. Generally,the thickness of the infrared ray reflective thin film is preferablyabout 50 to about 200 nm.

The optical waveguide thin film is, for example, a silica thin filmformed by the CVD method. The optical waveguide thin film may be formedin a desired pattern. The thickness of the optical waveguide film is,for example, about 50 to about 100 nm.

The transparent and electrically conductive thin film may be formed bythe sputtering or the ion plating of ITO, IXO, silver, chromium or thelike. Generally, the thickness of the transparent and electricallyconductive thin film is preferably about 0.1 to about 1 μm.

The fluorescent layer may be formed by the vacuum deposition of theorganic fluorescent material such as a low molecular weight dyematerial, or the layer may be formed by applying a fluid for coatingwhich is prepared by dispersing a binding agent and an inorganicfluorescent material such as Y₂O₃:Eu in pure water or an organicsolvent, followed by drying. Generally, the thickness of the fluorescentlayer is preferably about 0.1 to about 10 μm.

Examples of the aerogel substrates of which intermediate layer is thehydrophilic layer and the coating layer are schematically shown in FIGS.1(b) and 1(c). In the aerogel substrate shown in FIG. 1(b), the coatinglayer (2) is formed on a surface of the hydrophilic layer (not shown)which has been formed by subjecting one surface of the plate-likeaerogel layer (1) to the hydrophilicizing treatment and the functionallayer (3) is formed on the surface of the coating layer (2). The aerogelsubstrate shown in FIG. 1(c) is one in which the aerogel layer (1) isformed into a thin film on the plate member (100) which is, for example,a glass plate, and the coating layer (2) and the functional layer (3)are formed on the surface of the aerogel layer (1) in thus listed order.

Then, the aerogel substrate of the second embodiment in the firstaspect, i.e. the aerogel substrate in which the aerogel layer is thehydrophobic aerogel layer; the intermediate layer is the hydrophiliclayer which is formed by subjecting at least one surface of thehydrophobic aerogel layer to the hydrophilicizing treatment; and thefunctional layer is formed on the surface of the hydrophilic layer, isexplained.

This aerogel substrate corresponds to the aerogel substrate of the firstembodiment in the first aspect in which the coating is formed as thefunctional layer. In order to form the functional layer, it is necessaryto select the film-forming component(s) so that a desired function isimparted to the film. For example, a transparent and electricallyconductive thin-film is formed by selecting indium-tin oxide as thefilm-forming component. The aqueous fluid for coating which containsindium-tin oxide is obtained by adding a sol or a powder of indium-tinoxide fine particles into an aqueous solution of a polyvinyl alcohol ora polyethylene oxide or the like. A circuit board having the transparentand electrically conductive material thin film formed by application ofthe aqueous fluid for coating containing indium-tin oxide, can besufficiently practical depending on its application although itselectroconductivity tends to be smaller than that in the circuit boardhaving an indium-tin oxide thin film formed by the gas phase method suchas the sputtering.

One example of the aerogel substrate in which the intermediate layer isthe hydrophilic layer and the functional layer is formed on the surfaceof the hydrophilic layer is schematically shown in FIG. 1(a). Theaerogel substrate shown in FIG. 1(a) is one in which the hydrophiliclayer (not shown) is formed by subjecting one surface of the plate-likeaerogel layer (1) to the hydrophilicizing treatment and the functionallayer (3) is formed directly on the surface of the hydrophilic layer.

Then, the aerogel substrate of the third embodiment in the first aspect,i.e. the aerogel substrate in which the intermediate layer is theinorganic layer or the organic layer formed by the gas phase method isexplained. The meaning of “at least one surface” is the same asdescribed above in connection with the aerogel substrate of the firstembodiment in the first aspect, and therefore the detailed explanationthereof is omitted here.

As described above, since the gas phase method is a dry process, theaerogel layer which constitutes the aerogel substrate of the thirdembodiment in the first aspect may be one which has been subjected tothe hydrophobing treatment or one which has not been subjected to thehydrophobing treatment. Preferably, the aerogel layer has been subjectedto the hydrophobing treatment from a viewpoint of its durability. Whenthe aerogel substrate is used as a substrate for an electronic device oran EL (electroluminescence) device, it is generally used in a sealedcondition for dampproofing, and therefore the aerogel does not need tohave been subjected to the hydrophobing treatment.

The film formed by the gas phase method is provided to fill the pores inthe surface of the aerogel layer and preferably to further give a smoothsurface. The material which constitutes the film is either an organicmaterial or an inorganic material. Preferably, the material producesprecipitated particles which are smaller. It is necessary to form thefilm such that a residual energy in the film after the film formation issmall. When the residual energy after the film formation is large, thereoccurs a case where peeling of the film happens. The conditions forforming the film by the gas phase method are appropriately selecteddepending on the properties of the film-forming material(s) and theaerogel layer. For example, when it is desired to reduce the residualenergy or when the film is formed with the organic material, it ispreferable that a film formation temperature is low and the plasmaenergy is low. If densification of the film is difficult because of thelow film formation temperature, the film may be formed at a highertemperature.

The inorganic layer formed by the gas phase method is preferably made ofa material selected from SiO₂, SiN, SiON and TiO₂, and more preferablymade of SiO₂ (silica). The layer of silica is preferably formed by thesputtering method or the CVD method. When the layer of silica is formedas a thin film by the sputtering method, the film formation temperatureis preferably 20° C. to 400° C., and more preferably 150° C. to 250° C.When the layer of silica is formed by the CVD method, it is preferablethat the layer is formed using tetraethoxysilane as a starting materialat 100° C. to 400° C., and more preferably at 100° C. to 200° C.

The thickness of the inorganic layer is preferably 50 nm to 100 μm andmore preferably 50 nm to 1 μm.

The organic layer formed by the gas phase method is preferably preparedby the vacuum deposition. The organic layer can be formed by the vacuumdeposition of, for example, copper phthalocyanine, aluminum-quinolinolcomplex, or the like. A molecular weight of the organic compound forforming the organic layer is preferably smaller in order that thetemperature during the vapor deposition is low. When the organic layeris formed by the vapor deposition, the aerogel has preferably beensubjected to the hydrophobing treatment. The hydrophobicity of theaerogel improves adhesion between the organic layer and the aerogellayer, and allows the pores in the surface of the aerogel layer to befilled well (i.e. more densely).

The thickness of the organic layer is preferably 50 nm to 100 μm andmore preferably 50 nm to 1 μm.

The functional layer is formed on the surface of the inorganic layer orthe organic layer formed by the gas phase method. The inorganic ororganic layer provides a smooth surface by filling the pores in thesurface of the aerogel layer, and thereby the functional layer is formeduniformly thereon and performs its function effectively. The functionallayer is the same as described above in connection with the aerogelsubstrate of the first embodiment in the first aspect, and therefore thedetailed explanation thereof is omitted here.

The construction of the aerogel substrate of the third embodiment in thefirst aspect is as shown in FIGS. 1(b) and 1(c). When the aerogelsubstrate of the third embodiment in the first aspect has theconstruction as shown in FIG. 1(b), the inorganic layer or the organiclayer formed by the gas phase method is the layer denoted by the numeral“2”, and the functional layer is the layer which is formed on thesurface of the layer (2) and denoted by the numeral “3”. When theaerogel layer is formed on a surface of a plate member such as a glassplate, the aerogel substrate has the construction as shown in FIG. 1(c)in which the aerogel layer (1) as a thin film, the inorganic layer orthe organic layer (2) formed by the gas phase method, and the functionallayer (3) are laminated in thus listed order on the surface of the platemember (100).

The aerogel substrate of the fourth embodiment in the first aspectcomprises the aerogel layer, the welded layer which is formed by heatingat least one surface of the aerogel layer, and the functional layerwhich is formed on the surface of the welded layer. The meaning of “atleast one surface” is the same as described above in connection with theaerogel substrate of the first embodiment in the first aspect, andtherefore the detailed explanation thereof is omitted here.

The welded layer is formed by the annealing treatment in which thesurface of the aerogel layer is heated. The annealing treatment closesthe pores in the surface layer of the aerogel, and thereby the surfaceof the aerogel layer becomes dense and smooth suitable for forming thefunctional layer thereon. The annealing treatment is so carried out thatonly a surface layer portion of the aerogel layer is sintered, and theconditions of the treatment are appropriately selected depending on akind and a dimension of the aerogel. For example, in the case where theaerogel is a silica aerogel, the annealing treatment is carried out byplacing the silica aerogel into a high-temperature furnace at about 600°C. to about 1000° C. for several tens of seconds or by applying heatrays onto the surface of the silica aerogel layer for a short period oftime.

The thickness of the welded layer is preferably 50 nm to 100 μm.

The functional layer is formed on the surface of the welded layer. Thewelded layer provides a dense and smooth surface without pores, andthereby the functional layer is formed uniformly thereon and performsits function effectively. The functional layer is the same as describedabove in connection with the aerogel substrate of the first embodimentin the first aspect, and therefore the detailed explanation thereof isomitted here.

The aerogel a portion of which becomes the welded layer does not need tobe hydrophobic. However, it is preferably hydrophobic from the viewpointof its durability.

The construction of the aerogel substrate of the fourth embodiment inthe first aspect is the same as that of the aerogel substrate of thesecond embodiment in the first aspect, and has a construction, forexample, as shown in FIG. 1(a). When the aerogel substrate of the fourthembodiment in the first aspect has the construction as shown in FIG.1(a), the functional layer (3) is formed directly on the surface of thewelded layer (not shown) which has been formed by heating one surface ofthe plate-like aerogel layer (1).

The aerogel substrate of the fifth embodiment in the first aspectcomprises the aerogel layer, the Langmuir-Blodgett film which is formedon at least one surface of the aerogel layer, and the functional layerwhich is formed on the surface of the Langmuir-Blodgett film. Themeaning of “at least one surface” is the same as described above inconnection with the aerogel substrate of the first embodiment in thefirst aspect, and therefore the detailed explanation thereof is omittedhere.

As described above, the method for forming the polymer thin film by theLB method includes the vertical dipping method and the horizontaldipping method. In the case where the polymer thin film is formed by thevertical dipping method, the aerogel which has been subjected to thehydrophobing treatment is used in order to prevent break of themicroporous structure of the aerogel layer when it is dipped into water.According to the horizontal dipping method, the polymer thin film can beformed without contacting the aerogel layer with water. Therefore, whenthe horizontal dipping method is employed, the aerogel layer may be ahydrophilic aerogel layer. However, in order to prevent the break of themicroporous structure of the aerogel layer due to accidental contactbetween water and the aerogel layer, the aerogel which has beensubjected to the hydrophobing treatment is preferably used also when thehorizontal dipping method is applied. In any method, the aerogel layerwhich has been subjected to the hydrophobing treatment may be the one ofwhich surface has been subjected to the hydrophilicizing treatment.

The process for forming the polymer thin film on the surface of thehydrophobic aerogel layer by the horizontal dipping method is shown inFIG. 2. When a water-insoluble solution of an amphipatic polymer isspread on the water surface (10), each polymer molecule (11) is orientedparallel with one another on the water surface in a direction such thata hydrophilic portion (11 a) of the molecule (11) is in contact withwater (10) and a hydrophobic (lipophilic) portion (11 b) of the molecule(11) is out of contact with water, and thereby a polymer thin film (12)is formed as shown in FIG. 2(a). Then, a surface of the aerogel layer(1) is disposed horizontally and laid on the polymer thin film (12), andthereby the hydrophobic portion (11 b) of each polymer molecule (11)adheres to the hydrophobic surface of the aerogel layer (1). Next, bylifting up the aerogel layer (1), the polymer film (12) is transferredfrom the water surface to the surface of the aerogel layer (1) with thehydrophobic portion (11 b) of each polymer molecule (11) attached to thesurface of the aerogel layer (1), so that the LB film (2′) is formed onthe surface of the aerogel layer (1), as shown in FIG. 2(b). In the LBfilm (2′) of only one layer which is formed by this one time suchattachment operation, each polymer (11) constituting the LB (2′) is sooriented that the hydrophobic portion (11 b) faces to the aerogel layer(1) and the hydrophilic portion (11 a) faces in the opposite direction.Therefore, the surface of the LB film (2′) presents hydrophilicity sincethe hydrophilic portion (11 a) of each polymer (11) is exposed on thesurface of the LB film (2′).

FIG. 3 shows the process for forming the polymer thin film on thesurface of the hydrophobic aerogel layer by the vertical dipping method.When a water-insoluble solution of an amphipatic polymer is spread on awater surface (10), each polymer molecule (11) is oriented parallel withone another in the direction such that a hydrophilic portion (11 a) ofthe molecule (11) is in contact with water (10) and a hydrophobic(lipophilic) portion (11 b) of the molecule (11) is out of contact withwater, and thereby a polymer thin film (12) is formed on the watersurface in the same manner as described above, as shown in FIG. 3(a).Then, when the aerogel layer (1) is dipped into water with the surfaceof the aerogel layer (1) vertical to the water surface, the hydrophobicportion (11 b) of each polymer (11) adheres to the hydrophobic surfaceof the aerogel layer (1), and thereby the polymer thin film (12) isformed on the surface of the aerogel layer (1) such that the hydrophobicportions (11 b) face to the aerogel layer (1) and the hydrophilicportions (11 a) are disposed so as to be exposed on the surface as shownin FIG. 3(b). Therefore, the surface of the first polymer film (12)formed on the surface of the aerogel layer (1) presents hydrophilicity.Next, by drawing upward the aerogel layer (1) from water, the polymerfilm (12) on the water surface is so transferred that the hydrophilicportions (11 a) thereof adhere to the surface of the first polymer thinfilm (12) since the surface of the first polymer thin film (12) ishydrophilic. As a result, a polymer thin film (12) having a bilayerstructure is formed on the surface of the aerogel layer (1), as shown inFIG. 3(c). The hydrophobic portions (11 b) are exposed on the surface ofthe bilayer LB film (2′) formed in such manner, and thereby the surfaceof the LB film presents hydrophobicity.

The thickness of the LB film is preferably 0.001 to 0.1 μm. When thethickness is below 0.001 μm, no sufficiently smooth layer is formedbecause the ruggedness due to the pores in the surface of the aerogellayer appears on the surface of the LB film. When the thickness is above0.1 μm, it is difficult to utilize sufficiently the properties of theaerogel layer (such as a high heat insulating property, a highelectrically insulating property, a low refractive index, a lowdielectric constant and so on) in the aerogel substrate.

The functional layer is formed on a surface of the LB film. Since the LBfilm provides a smooth surface, the functional layer is formed uniformlyon the surface of the LB film and performs its function effectively. Inthe case where the LB film (2′) is hydrophilic, the functional layer canbe formed uniformly by a method in which an aqueous fluid for coating isapplied and thereafter dried. The functional layer is the same asdescribed above in connection with the aerogel substrate of the firstembodiment in the first aspect, and therefore the detailed explanationthereof is omitted here.

The aerogel substrate of the fifth embodiment in the first aspect has aconstruction, for example, as shown in FIGS. 1(b) and 1(c). When theaerogel substrate of the fifth embodiment in the first aspect has theconstruction as shown in FIG. 1(b), the LB film is the layer denoted bythe numeral “2” and the functional layer is the layer which is formed onthe surface of the layer (2) and denoted by the numeral “3”.When theaerogel layer is formed on a surface of a plate member such as a glassplate, the aerogel substrate has the construction as shown in FIG. 1(c)in which the aerogel layer (1) as a thin film, the LB film (2) and thefunctional layer (3) are laminated on the surface of the plate member(100) in thus listed order.

The aerogel substrate of the sixth embodiment in the first aspectcomprises the inorganic layered compound layer which is formed on atleast one surface of the aerogel layer, and the functional layer whichis formed on the surface of the inorganic layered compound layer. Themeaning of “at least one surface” is the same as described above inconnection with the aerogel substrate of the first embodiment in thefirst aspect, and therefore the detailed explanation thereof is omittedhere.

In the inorganic layered compound layer, plural layers of the inorganiccompound are superposed one upon another (or the other). The inorganiclayered compound layer is formed by having the surface of the aerogellayer adsorb the inorganic layered compound. As described above, thesolvent in which the inorganic layered compounds are dispersed is notinvolved in the formation of the layer during the process of theadsorption of the inorganic layered compound. Therefore, the inorganiclayered compound layer does not contain water even if the inorganiclayered compound layer is formed by dispersing the inorganic layeredcompound in, for example, water followed by contacting the surface ofthe aerogel layer with such water to form the inorganic layered compoundlayer and thereafter taking out the aerogel layer from water.

The adsorption of the inorganic layered compound by the aerogel layeroccurs by the Coulomb force acting between charges on the surface of theaerogel layer and charges on cleavage planes formed by cleavage of theinorganic layered compound in the solvent. The thickness of theinorganic layered compound layer formed on the surface of the aerogellayer is usually several nanometers because the inorganic layeredcompound is adsorbed by the surface of the aerogel layer in an amountwhich is necessary for counteracting the charges on the surface of theaerogel layer and because the cleavage generally occurs with the severalmolecules superposed one upon another. When the inorganic layeredcompound can be cleft into a monomolecule, the thickness of theinorganic layered compound layer is about 1 nm, and even if theinorganic layered compound layer has such a thickness, it can provide asmooth surface suitable for forming the functional layer thereon.

The inorganic layered compound is adsorbed by the surface of the aerogellayer by contacting the aerogel layer with a treatment liquid in whichthe inorganic layered compound is dispersed in a solvent. The aerogellayer may be contacted with the treatment liquid by, for example, beingdipped in the treatment liquid. The concentration of the inorganiclayered compound in the treatment liquid is 1% by mass or below suchthat the inorganic layered compound can cleave. The lower theconcentration of the inorganic layered compound is, the higher thedegree of dispersion is. However, if the concentration of the inorganiclayered compound is too low, it is difficult for the inorganic layeredcompound to be adsorbed by the aerogel layer. Therefore, theconcentration of the inorganic layered compound is preferably 0.001% bymass or more. In the case where the aerogel layer is dipped in thetreatment liquid, the aerogel (particularly silica aerogel) which hasbeen subjected to the hydrophobing treatment is preferably used in orderto prevent the break of the microporous structure of the aerogel layer.

A phyllosilicate mineral may be used as the inorganic layered compound,such as Na-montmorillonite, Ca-montmorillonite, synthetic smectite,Na-taeniolite, Li-taeniolite, Na-hectorite, Li-hectorite, acid clay,synthetic mica or the like. Water may be used as the solvent. The abovephyllosilicate mineral is swollen by penetration of a water moleculeinto the layered compound, and easily cleft into tabular materials ofwhich thickness is several nanometers and of which diameter in its planedirection is several tens to several hundreds nanometers when a force isapplied for example by the use of an ultrasonic or when the compoundconcentration of the treatment liquid is low. The inorganic layeredcompound layer may be made of one or more kinds of the inorganic layeredcompounds.

An ionic polymer may be attached to the surface of the aerogel layerbefore the inorganic layered compound layer is formed. The attachment ofthe ionic polymer makes it possible to increase the adhesion forcebetween the inorganic layered compound layer and the aerogel layer. Theionic polymer is not particularly limited as long as it is ionic. Acationic polymer such as a poly(allylaminehydrochloride), apoly(ethyleneimine) or a poly-(diallyldimethyl-ammoniumchloride), and ananionic polymer such as a poly(styrenesulfonate) or a poly(vinylsulfate)are exemplified as the ionic polymer. The ionic polymer is attached tothe surface of the aerogel layer by dipping the aerogel layer in anaqueous solution of the ionic polymer or by the LB method. Pluralinorganic layered compound layers can be formed on the surface of theaerogel layer by repeating the adhesion of the ionic polymer and theadsorption of the inorganic layered compound layer.

The thickness of the inorganic layered compound layer is preferably 0.01to 1 μm.

The functional layer is formed on the surface of the inorganic layeredcompound layer. The inorganic layered compound layer provides the smoothsurface, and thereby, the functional layer is formed uniformly thereonand performs its function effectively. The functional layer is the sameas described above in connection with the aerogel substrate of the firstembodiment in the first aspect, and therefore the detailed explanationthereof is omitted here.

The aerogel substrate of the sixth embodiment in the first aspect has aconstruction, for example, as shown in FIGS. 1(b) and 1(c). When theaerogel substrate of the sixth embodiment in the first aspect has theconstruction as shown in FIG. 1(b), the inorganic layered compound layeris the layer denoted by the numeral “2” and the functional layer is thelayer which is formed on the surface of the inorganic layered compoundlayer (2) and denoted by the numeral “3”.When the aerogel layer isformed on a surface of a plate member such as a glass plate, the aerogelsubstrate has the construction as shown in FIG. 1(c) in which theaerogel layer (1) as a thin film, the inorganic layered compound layer(2) and the functional layer (3) are laminated on the surface of theplate member (100) in thus listed order.

Effects which are given by the aerogel substrates and the process forproducing the same according to the present invention which aredescribed in the above are as follows:

The aerogel substrate comprises the aerogel layer, the intermediatelayer which is formed on at least one surface of the aerogel layer andthe functional layer which is formed on the surface of the intermediatelayer, the functional layer being formed on the surface of theintermediate layer without a material which constitutes the functionallayer penetrating into the aerogel layer. In this aerogel substrate, thematerial(s) which constitutes the functional layer does not penetrateinto the aerogel layer, and therefore the functional layer constitutesthe aerogel substrate as a uniform layer of which surface is continuouswith a small surface roughness, and performs a predetermined functionwell.

In the aerogel substrate of the present invention, the intermediatelayer is preferably the layer which prevents the material(s)constituting the functional layer from penetrating into the aerogellayer. Such intermediate layer makes it possible to form a uniform andthin functional layer on the surface of the aerogel layer by theconventional method.

The aerogel substrate of the present invention is realized by using thehydrophobic aerogel layer as the aerogel layer and forming theintermediate layer of the hydrophilic layer which is obtained bysubjecting the surface of the hydrophobic aerogel layer to thehydrophilicizing treatment; and the coating layer formed on the surfaceof the hydrophilic layer. Such aerogel substrate is characterized inthat only the surface of the hydrophobic aerogel layer has beenhydrophilicized by the plasma treatment or the UV ozone treatment andthe inside thereof remains hydrophobic. This characteristic makes itpossible to uniformly coat the surface of the aerogel layer with theaqueous fluid for coating to form the uniform thin film on the surfaceof the hydrophobic aerogel layer. Further, no aqueous fluid for coatingpenetrates into the aerogel layer to break the microporous structurethereof. The film formed with the aqueous fluid for coating provides thesmooth surface and allow the functional layer to be formed uniformly onthe surface.

The aerogel substrate of the present invention is preferably realized bythe aerogel substrate in which the hydrophobic aerogel layer is used asthe aerogel layer; the intermediate layer is the hydrophilic layer whichis formed by subjecting the surface of the hydrophobic aerogel layer tothe hydrophilicizing treatment; and the functional layer is the coatinglayer formed on the surface of the hydrophilic layer. Such aerogelsubstrate is characterized in that the surface of the hydrophobicaerogel layer is hydrophilicized so that the functional layer may beformed directly on the surface of the aerogel layer. This aerogelsubstrate is a variation of the aerogel substrate of the firstembodiment and it can be produced by fewer steps than the aerogelsubstrate of the first embodiment.

Further, the aerogel substrate of the present invention is preferablyrealized by the aerogel substrate in which the intermediate layer is theinorganic layer or the organic layer formed by the gas phase method. Thegas phase method which is a dry process makes it possible to form thethin film having the smooth surface as the intermediate layer on thesurface of the aerogel layer without breakage of the microporousstructure of the aerogel due to a liquid substance. The inorganic layeror the organic layer fills the pores in the surface of the aerogel layerto provide the smooth surface, and thereby the functional layer can beformed uniformly on the surface of the inorganic or organic layer.

Further, the pores in the surface of the aerogel are surely filled andthe unevenness of the surface of the aerogel layer is “evened out”effectively by the gas phase method since the method can easily controlthe thickness of the film (layer) to be formed.

In the aerogel substrate in which the layer formed by the gas phasemethod is made of silica, the adhesion force between the aerogel layerand the silica film is large, and the pores in the surface of theaerogel layer are filled better. Thus, when the layer made of silica isformed by the gas phase method, a smoother surface is formed, andtherefore, the aerogel substrate is obtained in which the functionallayer is formed more uniformly. This is also applicable to the casewhere the layer formed by the gas phase method is made of SiN, SiON orTiO₂.

The aerogel substrate of the present invention is preferably realized bythe aerogel substrate in which the intermediate layer is the weldedlayer formed by heating the surface of the aerogel layer. The weldedlayer provides the dense and smooth surface formed by closing the poresin the surface of the aerogel. Therefore, the welded layer makes itpossible to form the functional layer uniformly thereon.

The aerogel substrate of the present invention is preferably realized bythe aerogel substrate in which the intermediate layer is theLangmuir-Blodgett film. The Langmuir-Blodgett film provides the smoothsurface suitable for forming the functional thin film thereon. TheLangmuir-Blodgett film is formed without breaking the microporousstructure of the aerogel layer. Further, the thickness of the LB filmcan be very thin, for example several nanometers thickness if necessary,and controlled by a nanoscale by varying a length of the side-chain ofthe polymer. Therefore, no degradation of the function of the functionallayer due to the thick layer between the functional layer and theaerogel layer is caused in the aerogel substrate comprising theLangmuir-Blodgett film.

The aerogel substrate of the present invention is realized also by theaerogel substrate in which the intermediate layer is the inorganiclayered compound layer. The solvent is not involved in the formation ofthe inorganic layered compound layer when the layer is formed.Therefore, the inorganic layered compound layer is formed on either thehydrophobic aerogel layer or the hydrophilic aerogel layer to providethe smooth surface, and makes it possible to form the functional layeruniformly.

In the aerogel substrate of the present invention, in the case where theaerogel is the silica aerogel, moisture adsorption by the aerogel layeris prevented, and therefore deterioration of the various properties ofthe aerogel due to aging is prevented.

In the aerogel substrate of the present invention, in the case where thefunctional layer is the thin film of the electrically conductivematerial, the circuit board in which the low dielectric constant of theaerogel, particularly the silica aerogel is utilized is obtained.

In the aerogel substrate of the present invention, in the case where thefunctional layer is the infrared ray reflective thin film, the heatinsulating substrate in which the low thermal conductivity of theaerogel, particularly the silica aerogel is utilized is obtained.

In the aerogel substrate of the present invention, in the case where thefunctional layer is the optical waveguide thin film, the opticalwaveguide substrate in which the low refractive index of the aerogel,particularly the silica aerogel is utilized is obtained.

In the aerogel substrate of the present invention, in the case where thefunctional layer is the transparent and electrically conductive thinfilm, the transparent and electrically conductive thin film substrate inwhich the low refractive index of the aerogel, particularly the silicaaerogel is utilized is obtained.

In the aerogel substrate of the present invention, in the case where thefunctional layer is the fluorescent layer, the light emitting device inwhich the low refractive index of the aerogel, particularly the silicaaerogel is utilized is obtained.

INDUSTRIAL APPLICABILITY

The aerogel substrate of the present invention effectively presentsproperties of the functional layer coupled with properties of theaerogel, and can be applied as a high performance substrate in variousfields such as an electronics field. Depending on the kinds of thefunctional layers, the aerogel substrate of the present invention can beused as the electrically conductive substrate, the heat insulatingsubstrate, the optical waveguide substrate, the substrate for the lightemitting device, or the light emitting device. These substrates aresuitable for constituting a CRT, an FED, an inorganic EL device, anorganic EL device, a plasma display panel, a flat fluorescent lamp, anLCD and so on. The process for producing the aerogel substrate of thepresent invention makes it possible to form the functional layeruniformly on the surface of the aerogel layer on which it has beendifficult to form a thin film. Therefore, the production process of theaerogel substrate according to the present invention is also a usefulprocess for forming a thin film in which process a desired thin film isformed uniformly on a surface of the aerogel.

EXAMPLES

The present invention will be, hereinafter, explained more concretelywith reference to the following Examples.

Example 1

An aerogel substrate having a construction as shown in FIG. 1(c) wasproduced according to the following procedures.

Solution A was prepared by mixing an oligomer of tetramethoxysilane(manufactured by Colcoat Co. Ltd., trade name “Methylsilicate 51”)andmethanol at a mass ratio of 47:81. Further, Solution B was prepared bymixing water, 28% by mass ammonia aqueous solution and methanol at amass ratio of 50:1:81. Then, Solution A and Solution B were mixed at amass ratio of 16:17 to form an alkoxysilane solution, which was droppedonto one surface of a plate member (100) made of soda glass followed byspin-coating at 700 r.p.m. for ten seconds. Then, after gelation of thealkoxysilane to produce a gel compound, the plate with gel was dippedinto an aging solution which contained water, 28% by mass ammoniaaqueous solution and methanol at a mass ratio of 162:4:640 to age thegel compound for one day at room temperature. Next, the gel compound inthe form of a thin film aged as described above was dipped in anisopropanol solution containing 10% by mass of hexamethyldisilazane soas to carried out the hydrophobing treatment. The gel compound in theform of the thin film thus formed on the surface of the glass plate wasdipped in the isopropanol so as to wash the gel compound. Then, the gelcompound was placed in a autoclave, which was filled with liquefiedcarbon dioxide, and then the gel compound was dried by the supercriticaldrying under conditions of 80° C. and 16 MPa, whereby a thin film ofsilica aerogel (1) of which thickness was 30 μm was formed on thesurface of the glass plate (100).

A silica thin film (2) of which thickness was 100 nm was formed on thesurface of the silica aerogel thin film (1). The silica thin film wasformed by the deposition using tetraethoxysilane through the CVD methodunder conditions of 200° C., 3 Pa and 700 W. Next, a transparent andelectrically conductive thin film (3) of IXO of which thickness was 200nm was formed on the surface of the silica thin film (2) by thesputtering under conditions of room temperature, 0.7 Pa and 100 W,whereby a substrate for an EL light emitting device was produced.

Example 2

An aerogel substrate having a construction as shown in FIG. 1(c) wasproduced according to the following procedures.

A silica aerogel thin film (1) was formed on one surface of a soda glassplate (100) in the same manner as in Example 1. Next, a silica thin film(2) of which thickness was 100 nm was formed on the surface of thesilica aerogel thin film (1). The silica thin film (2) was formed by thesputtering method under conditions of 200° C., 0.7 Pa and 300 W. Then, atransparent and electrically conductive thin film (3) of ITO of whichthickness was 200 nm was formed on the surface of the silica thin film(2) by the sputtering under conditions of 200° C., 1 Pa and 300 W,whereby a substrate for an EL light emitting device was produced.

Example 3

An aerogel substrate having a construction as shown in FIG. 1(c) wasproduced according to the following procedures.

A silica aerogel thin film (1) was formed on one surface of a soda glassplate (100) in the same manner as in Example 1. Next, a copperphthalocyanine thin film (2) of which thickness was 50 nm was formed onthe surface of the silica aerogel thin film (1) by the vacuumdeposition. Then, an Al thin film as an electrically conductive thinfilm (3) of which thickness was 50 nm was formed on the surface of thecopper phthalocyanine thin film by the vacuum deposition, whereby asubstrate for a circuit board was produced.

Example 4

An aerogel substrate having a construction as shown in FIG. 1(c) wasproduced according to the following procedures.

A silica aerogel thin film (1) was formed on one surface of a soda glassplate (100) in the same manner as in Example 1. Next, a hydrophiliclayer (not shown) of which thickness was 50 nm was formed by subjectingthe surface of the silica aerogel thin film (1) to the plasma treatmentin a helium/argon/oxygen atmosphere by means of the atmospheric pressureplasma technique using an electric power of 700 W. Then, an aqueousfluid for coating containing 10% by mass of silica and 10% by mass of apolyvinyl alcohol was prepared by dissolving the polyvinyl alcohol anddispersing a silica sol. This fluid was applied onto the surface of thesilica aerogel thin film (1), and then dried at 105° C., whereby asilica thin film (2) of which thickness was 50 nm was formed. Next, anIXO thin film as a transparent and electrically conductive thin film (3)of which thickness was 200 nm was formed on the surface of the silicathin film (2) by the sputtering under conditions of room temperature,0.7 Pa and 100 W, whereby a substrate for an EL light emitting devicewas produced.

Comparative Example 1

Without formation of the silica thin film, an IXO thin film was formedin the same manner as in Example 1 on the surface of the silica aerogelthin film which was formed in the same manner as in Example 1 on onesurface of the soda glass, whereby a substrate for a light emittingdevice was produced.

Comparative Example 2

Without formation of the silica thin film, an ITO thin film was formedin the same manner as in Example 2 on the surface of the silica aerogelthin film which was formed in the same manner as in Example 1 on onesurface of the soda glass, whereby a substrate for a light emittingdevice was produced.

Comparative Example 3

Without formation of the copper phthalocyanine thin film, an Al thinfilm was formed in the same manner as in Example 3 on the surface of thesilica aerogel thin film which was formed in the same manner as inExample 1 on one surface of the soda glass, whereby a circuit board wasproduced.

An electrical conductivity per 1 cm distance on the outermost surface ofthe aerogel substrates produced in Examples 1 to 4 and ComparativeExamples 1 to 3 was measured with a tester. The results are shown inTable 1 below:

TABLE 1 1 cm Intermediate Functional electric layer layer resis- Aerogel(Formation (Formation tance layer method) method) (Ω) Example Silicaaerogel Silica thin film IXO thin film 40 1 thin film (CVD) (Sputtering)Example Silica aerogel Silica thin film ITO thin film 30 2 thin film(Sputtering) (Sputtering) Example Silica aerogel Copper Al thin film 0.33 thin film phthalocyanine (Vacuum thin film deposition) (Vacuumdeposition) Example Silica aerogel Hydrophilic layer IXO thin film 50 4thin film (Plasma (Sputtering) treatment)/ Silica + PVA (Coating)Compara- Silica aerogel — IXO thin film K to M tive thin film(Sputtering) order Example 1 Compara- Silica aerogel — ITO thin film Kto M tive thin film (Sputtering) order Example 2 Compara- Silica aerogel— Al thin film 70 tive thin film (Vacuum Example deposition) 3

Example 5

An aerogel substrate having a construction as shown in FIG. 1(c) wasproduced according to the following procedures.

A silica aerogel thin film (1) was formed on one surface of a soda glassplate (100) in the same manner as in Example 1 except that the rotationnumber of the spin coating was 2000 r.p.m and the thickness of thesilica aerogel thin film was 1 μm. Next, a hydrophilic layer of whichthickness was 50 nm was formed by subjecting the surface of the silicaaerogel thin film (1) to the plasma treatment in a helium/argon/oxygenatmosphere by means of the atmospheric pressure plasma technique using aelectric power of 700 W. Then, an aqueous fluid for coating containing10% by mass of silica and 10% by mass of a polyvinyl alcohol wasprepared by dissolving the polyvinyl alcohol and dispersing a silicasol. This fluid was applied onto the surface of the silica aerogel thinfilm (1), and then dried at 105° C., whereby a silica thin film (2) ofwhich thickness was 50 nm was formed. Then, the fluorescent layer (3) ofwhich thickness was 100 nm was formed on a surface of the silica thinfilm (2) by the vacuum deposition of aluminum-quinolinol complex(tris(8-quinolinolate)aluminum manufactured by Dojindo Laboratories),whereby a light emitting device was produced.

Example 6

An aerogel substrate having a construction as shown in FIG. 1(b) wasproduced according to the following procedures.

An alkoxysilane solution which was prepared in the same manner as inExample 1 was cast in a styrene resin made mold and the mold was closedfollowed by being allowed to stand for gelation and then aging of thealkoxysilane at room temperature. Next, the hydrophobing treatment andthe supercritical drying were carried out in the same manner as Example1 to form a silica aerogel plate (1) of which thickness was 5 mm.

Then, a welded layer of which thickness was 50 nm was formed by theannealing treatment in which one surface of the silica aerogel plate (1)was heated. The heating was carried out by placing the aerogel plateinto a furnace at 600° C. for 30 seconds. Then, the aerogel plate wastaken out from the furnace and allowed to cool. Next, a fluorescentlayer (3) of which thickness was 100 nm was formed on the surface of thewelded layer by the vacuum deposition of aluminum-quinolinol complex(tris(8-quinolinolate)aluminum manufactured by Dojindo Laboratories),whereby a light emitting device was produced.

Comparative Example 4

Without formation of the silica thin film, a fluorescent layer wasformed in the same manner as in Example 5 on the surface of silicaaerogel thin film which was formed on one surface of a soda glass platein the same manner as in Example 5.

Each of thin film substrates produced in Examples 5 and 6 andComparative Example 4 was irradiated with black light of 20 W and aluminance of each substrate was measured. The results are shown in Table2 below.

TABLE 2 Intermediate layer Functional layer Average Aerogel (Formation(Formation luminance layer method) method) (cd/cm²) Example 5 SilicaSilica/PVA aluminum- 2.2 aerogel (Coating) quinolinol thin film (Vacuumdeposition) Example 6 Silica Welded layer aluminum- 2.6 aerogelquinolinol plate (Vacuum deposition) Compara- Silica — aluminum- 1.5tive aerogel quinolinol Example 4 thin film (Vacuum deposition)

Example 7

An aerogel substrate having a construction as shown in FIG. 1(c) wasproduced according to the following procedures.

A silica aerogel thin film (1) of which thickness was 1 mm was formed onone surface of a soda glass plate (100) in the same manner as inExample 1. Next, a silica thin film (2) of which thickness was 100 nmwas formed in the same manner as in Example 1 on the surface of thesilica aerogel thin film (1). Then, an Al thin film of which thicknesswas 50 nm was formed as an infrared ray reflective thin film (3) in thesame manner as in Example 3 on the surface of the silica thin film,whereby a heat insulating substrate was produced.

Example 8

An aerogel substrate having a construction as shown in FIG. 1(b) wasproduced according to the following procedures.

A silica aerogel plate of which thickness was 5 mm was produced in thesame manner as in Example 6. Next, a silica thin film (2) of whichthickness was 100 nm was formed in the same manner as in Example 1 onthe surface of the silica aerogel plate (1). Then, an Al thin film (3)of which thickness was 50 nm was formed as an infrared ray reflectivethin film in the same manner as in Example 3 on the surface of thesilica thin film, whereby a heat insulating substrate was produced.

Comparative Example 5

An Al thin film of which thickness was 50 nm was formed as an infraredray reflective thin film in the same manner as in Example 3 on onesurface of a soda glass plate which surface did not have a silica thinfilm thereon, whereby a heat insulating substrate was produced.

Comparative Example 6

Without formation of the silica thin film, an Al thin film having athickness of 50 nm was formed as an infrared ray reflective thin film inthe same manner as in Example 3 on one surface of a silica aerogel platehaving a thickness of 5 mm which was formed in the same manner as inExample 6, whereby a heat insulating substrate was produced.

As to each of the thin film substrates produced in Examples 7 and 8 andComparative Examples 5 and 6, a thermal conductivity was measuredaccording to ASTM and a transmittance of an infrared ray having awavelength of 1000 nm was measured with a spectrophotometer. The resultsare shown in Table 3 below.

TABLE 3 IR Intermediate Functional Ther- trans- layer layer mal mit-Aerogel (Formation (Formation cond. tance layer method) method) (W/mk)(%) Example 7 Silica Silica thin film Al thin film 0.35 20 aerogel (CVD)(Vacuum thin film deposition) Example 8 Silica Silica thin film Al thinfilm 0.013 18 aerogel (CVD) (Vacuum thin film deposition) Compara- — —Al thin film 1.3 18 tive (Vacuum Example 5 deposition) Compara- Silica —Al thin film 0.013 55 tive aerogel (Vacuum Example 6 thin filmdeposition)

Example 9

An aerogel substrate having a construction as shown in FIG. 1(b) wasproduced according to the following procedures.

A hydrophobic silica aerogel thin film (1) of which thickness was 20 μmwas formed on one surface of a soda glass plate (100) in the same manneras in Example 1. Next, the silica aerogel thin film (1) with the glassplate (100) was dipped in an aqueous solution containing 5.0% by mass ofa poly(diallyldimethylammoniumchloride) for 10 minutes followed by beingdipped in pure water for 10 minutes, and thereby thepoly(diallyidimethyl-ammoniumchloride) as an ionic polymer was attachedto the surface of the silica aerogel thin film (1). Then, the aerogelthin film (1) with the glass plate (100) was dipped in a treatmentliquid in which synthetic hectorite (manufactured by Laporte Kogyo,trade name “Laponite RD”)was dispersed in water at a concentration of0.2% by mass by the vertical dipping method and allowed to stand for 10minutes followed by being dipped in pure water for 10 minutes, andthereby an inorganic layered compound layer (2) of the synthetichectorite of which thickness was 0.01 μm was formed. Then, an ITO thinfilm as a transparent and electrically conductive thin film (3) of whichthickness 100 nm was formed on one surface of the inorganic layeredcompound layer (2) by the sputtering under conditions of 200° C., 1 Paand 100 W, whereby a substrate for a light emitting device was produced.

Comparative Example 7

A substrate for a light emitting device was produced in the same manneras in Example 9 except that no ionic polymer was attached and noinorganic layered compound layer was formed.

An electrical conductivity per 1 cm distance on the outermost surface ofthe aerogel substrates produced in Example 9 and Comparative Example 5was measured with a tester. The results are shown in Table 4 below:

TABLE 4 Functional 1 cm layer electric Aerogel Intermediate (Formationresistance layer layer method) (Ω) Example 9 Silica aerogel Ionic ITOthin film 30 thin film polymer/ (Sputtering) Inorganic layered compoundlayer Compara- Silica aerogel — ITO thin film K to M tive thin film(Sputtering) order Example 7

Example 10

An aerogel substrate having a construction as shown in FIG. 1(c) wasproduced according to the following procedures.

A hydrophobic silica aerogel thin film (1) of which thickness was 10 μmwas formed on one surface of the soda glass plate (100) in the samemanner as in Example 1. Next, an LB film (2) of which thickness was 10nm was formed on the surface of the aerogel thin film (1) by attaching apolyvinyl octanal acetal to the surface by the vertical dipping methodat a surface pressure of 25 mN/m. The LB film (2) was formed of a singlelayer of the polymer and its surface was hydrophilic. Then, an IXO thinfilm (3) of which thickness was 200 nm was formed as an electricallyconductive thin film on the surface of the LB film (2) by the sputteringunder conditions of room temperature, 0.7 Pa and 100 W, whereby asubstrate for a light emitting device was produced.

Example 11

A substrate for a light emitting device was produced in the same manneras in Example 10 except that an ITO film (3) as an electricallyconductive thin film of which thickness was 200 nm was formed on thesurface of the LB film (2) by the sputtering under conditions of 200°C., 1 Pa and 300 W.

Example 12

An aerogel substrate having a construction as shown in FIG. 1(c) wasproduced according to the following procedures.

A hydrophobic silica aerogel thin film (1) of which thickness was 20 μmwas formed on one surface of a soda glass plate (100) in the same manneras in Example 1. Next, a polymer thin film of which thickness was 10 nmwas formed on the surface of the hydrophobic aerogel thin film (1) byattaching a polyvinyl octanal acetal to the surface by the verticaldipping method at a surface pressure of 25 mN/m. Further, anotherpolymer thin film of which thickness was 10 nm was formed by attaching apolyvinyl octanal acetal to the surface of the polymer film by thevertical dipping method at a surface pressure of 25 mN/m. As a result, atwo-layer LB film (2) of which surface was hydrophobic was formed on thesurface of the hydrophobic silica aerogel thin film. Next, an ITO film(3) as an electrically conductive thin film of which thickness 200 nmwas formed on the surface of the LB film (2) by the sputtering underconditions of 200° C., 1 Pa and 300 W, whereby a substrate for a lightemitting device was produced.

Comparative Example 8

A substrate for a light emitting device was produced in the same manneras in Example 10 except that no LB film was formed.

Comparative Example 9

A substrate for a light emitting device was produced in the same manneras in Example 11 except that no LB film was formed.

An electrical conductivity per 1 cm distance on the outermost surface ofthe aerogel substrates produced in Examples 10 to 12 and ComparativeExamples 6 and 7 was measured with a tester. The results are shown inTable 5 below:

TABLE 5 Functional 1 cm layer electric Aerogel Intermediate (Formationresistance layer layer method) (Ω) Example Silica aerogel LB film IXOthin film 50 10 thin film (Sputtering) Example Silica aerogel LB filmITO thin film 30 11 thin film (Sputtering) Example Silica aerogel LBfilm ITO thin film 10 12 thin film (two (Sputtering) layers) Compara-Silica aerogel — IXO thin film K to M tive thin film (Sputtering) orderExample 8 Compara- Silica aerogel — ITO thin film K to M tive thin film(Sputtering) order Example 9

Example 13

An aerogel substrate having a construction as shown in FIG. 1(b) wasproduced according to the following procedures.

A hydrophobic silica aerogel thin film (1) of which thickness was 30 μmwas formed on one surface of a soda glass plate (100) in the same manneras in Example 1. Next, a hydrophilic layer (not shown) of whichthickness was 50 nm was formed on the surface of the silica aerogel bysubjecting the surface of the silica aerogel thin film (1) to the plasmatreatment in a helium/argon/oxygen atmosphere through the atmosphericpressure plasma technique using an electric power of 700 W. Then, anaqueous fluid for coating containing 30% by mass of indium-tin oxide and3% by mass of a polyvinyl alcohol was prepared by dissolving thepolyvinyl alcohol and dispersing indium-tin oxide powder. This fluid wasapplied onto the surface of the silica aerogel thin film (1), and thencalcinated at 600° C., whereby an ITO thin film of which thickness was 2μm was formed as a transparent and electrically conductive thin film(3).

An electrical conductivity per 1 cm distance on the outermost surface ofthe aerogel substrates produced in Example 13 was measured with atester. The results are shown in Table 6 below:

TABLE 6 Functional 1 cm layer electric Aerogel Intermediate (Formationresistance layer layer method) (Ω) Example Silica aerogel HydrophilicITO thin film 200 13 thin film layer (Coating)

What is claimed is:
 1. An aerogel substrate, comprising an aerogellayer, an intermediate layer formed on a surface of the aerogel layer,and a functional layer formed on a surface of the intermediate layerwithout penetration into the aerogel layer, wherein the functional layeris an infrared ray reflective thin film; an optical waveguide thin film;a transparent and electrically conductive thin film comprising at leastone member selected from the group consisting of indium-tin oxide,indium-zinc oxide, silver, and chromium; a fluorescent layer; or anelectrically conductive thin film; provided that when the functionallayer is an electrically conductive thin layer, then the intermediatelayer is copper phthalocyanine.
 2. The aerogel substrate according toclaim 1, wherein the intermediate layer prevents the material whichconstitutes the functional layer from penetrating into the aerogellayer.
 3. The aerogel substrate according to claim 2, wherein theaerogel layer comprises a hydrophobic aerogel layer, the intermediatelayer comprises a hydrophilic layer and a coating layer, wherein thehydrophilic layer is formed by subjecting a surface of the hydrophobicaerogel layer to a hydrophilicizing treatment, the coating layer isformed on a surface of the hydrophillic layer, and wherein thefunctional layer is formed on a surface of the coating layer.
 4. Theaerogel substrate according to claim 2, wherein the intermediate layercomprises at least one member selected from the group consisting of aninorganic layer or an organic layer, wherein the inorganic layer and theorganic layer are formed by a gas phase method.
 5. The aerogel substrateaccording to claim 4, wherein the inorganic layer is made of aninorganic material selected from SiO2, SiN, SiON and TiO2.
 6. Theaerogel substrate according to claim 2, wherein the intermediate layeris a welded layer which is formed by heating at least one surface of theaerogel layer.
 7. The aerogel substrate according to claim 2, whereinthe intermediate layer is a Langmuir-Blodgett film.
 8. The aerogelsubstrate according to claim 2, wherein the intermediate layer comprisesat least one inorganic layer.
 9. The aerogel substrate according toclaim 1, wherein the aerogel layer is a hydrophobic aerogel layer, theintermediate layer is a hydrophilic layer which is formed by subjectinga surface of the hydrophobic aerogel layer to a hydrophilicizingtreatment, and the functional layer is formed on a surface of thehydrophilic layer.
 10. The aerogel substrate according to claim 1,wherein the aerogel is a silica aerogel.
 11. The aerogel substrateaccording to claim 1, wherein the aerogel layer is formed on a platemember.
 12. The aerogel substrate according to claim 1, wherein thefunctional layer comprises at least one member selected from the groupconsisting of aluminum-quinolinol, Y₂O₃:Eu, LaPO₄:Ce, Tb, andBaMGAL₁₀O₁₇:Eu.
 13. A process for producing the aerogel substrateaccording to claim 3 comprising the steps of forming a hydrophilic layerby subjecting at least one surface of an aerogel layer to a plasmatreatment or a UV ozone treatment; and forming a functional layer bycoating a surface of the hydrophilic layer with an aqueous solutionand/or an aqueous dispersion of a film-forming component followed bydrying the solution and/or the dispersion.
 14. The process according toclaim 13, wherein the aerogel is a silica aerogel.
 15. The processaccording to claim 13 wherein the functional layer is formed by acoating method or gas phase method.
 16. A process for producing anaerogel substrate having a functional layer on at least one surfacethereof comprising the steps of: forming an intermediate layer on atleast one surface of an aerogel layer; and forming a functional layer ona surface of the intermediate layer, said intermediate layer being alayer which prevents a material which constitutes the functional layerfrom penetrating into the aerogel layer, wherein the functional layer isan infrared ray reflective thin film; an optical waveguide thin film; atransparent and electrically conductive thin film comprising at leastone member selected from the group consisting of indium-tin oxideindium-zinc oxide, silver, and chromium; a fluorescent layer; or anelectrically conductive thin film; provided that when the functionallayer is an electrically conductive thin layer, then the intermediatelayer is copper phthalocyanine.
 17. The process according to claim 16,wherein forming the intermediate layer comprises the steps of: forming ahydrophilic layer by subjecting at least one surface of a hydrophobicaerogel layer to a plasma treatment or a UV ozone treatment; and forminga coating layer by coating a surface of the hydrophilic layer with anaqueous solution and/or an aqueous dispersion of a film-formingcomponent followed by drying the solution and/or the dispersion.
 18. Theprocess according to claim 16, wherein the step of forming theintermediate layer comprises the step of forming an inorganic layer oran organic layer by a gas phase method on at least one surface of theaerogel layer.
 19. The process according to claim 18, wherein the gasphase method is selected from a CVD method, a sputtering method and avapor deposition method.
 20. The process according to claim 16, whereinthe step of forming the intermediate layer comprises the step of forminga welded layer by heating at least one surface of the aerogel layer. 21.The process according to claim 16, wherein the step of forming theintermediate layer comprises the step of forming a thin film on at leastone surface of the aerogel layer by the Langmuir-Blodgett method. 22.The process according to claim 16, wherein the step of forming theintermediate layer comprises the step of forming an inorganic layeredcompound layer by having at least one surface of an aerogel layer adsorban inorganic layered compound.
 23. The process according to claim 16,wherein the aerogel is a silica aerogel.
 24. The process according toclaim 16, wherein the functional layer is formed by a coating method ora gas phase method.
 25. The process according to claim 16, wherein thefunctional layer comprises at least one member selected from the groupconsisting of aluminum-quinolinol, T₂O₃:Eu, LaPO₄:Ce, Tb, andBaMGAL₁₀O₁₇:Eu.